Process of protecting synthetic protein fibers during steaming and bleaching by applying sodium oxalate



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PROCESS OF PROTECTING SYNTHETIC PROTEIN FIBERS DURING STEAMING AND BLEACHING BY APPLYING SODIUM OXALATE Arnold Maurice Sookne, Silver Spring, Md., and Agnes Eleanor Davis, Arlington, Va., assignors to Virginia- Carolina Chemical Corporation, Richmond, Va., a corporation of Virginia N Drawing. Application March 18, 1954 Serial No. 417,228

4 Claims. (Cl. 8-133) This invention relates to an improvement in the aqueous heat treatment of synthetic protein fibers.

By aqueous heat treatment we mean treatments such as steaming, dyeing, crimping, bleaching and the like in which the fibers are subjected to the action of water or aqueous solutions and/ or steam at temperatures approaching or exceeding 100 C., e. g. from about 90 C. to about 105 C.

The principal improvement accomplished by the invention is an improvement in the mechanical properties, particularly the strength properties, of the fibers.

While the invention is believed to be applicable to all synthetic protein fibers in the sense that the improvement to be described tends to preserve the mechanical properties of the fibers we wish to point out that commercial synthetic casein fibers available at present are not capable of withstanding severe aqueous heat treatment either with or without the improvement afiorded by the invention. For practical purposes therefore the invention is to be regarded as being limited to such synthetic protein fibers as are capable of maintaining their integrity under the conditions of the aqueous heat treatment applied which, in the case of synthetic casein fibers, must be limited to mild conditions i. e. low temperature and/ or limited time and/or mild treating agents which will not destroy the fibers.

Processes which involve treatment of synthetic protein fibers at high temperatures in the presence of moisture produce serious degradation of the fiber. As an example of this a sample of commercial zein fiber which originally had a dry tensile strength of 1.18 grams per denier and an ultimate elongation of 38%, after steaming for 90 minutes at a pH of 7 had a resultant tensile strength of 0.95 gram per denier and a resultant ultimate elongation of 52%. The same fiber after a conventional peroxide bleaching treatment at a pH of 8 with 9% hydrogen peroxide, had a resultant tensile strength of 0.47 gram per denier and the resultant sample was so embrittled by the treatment that the ultimate elongation could not be determined. This loss of mechanical properties when synthetic protein fibers are subjected to the various aqueous heat treatments is a serious hindrance to their acceptance in normal textile markets.

It is an object of this invention to provide a method to retain the mechanical properties of synthetic protein fibers when they are subjected to normal aqueous heat treatments. It is also an object to provide a simple, economical method which will not involve additional equipment or added process steps to the present normal practices of the textile fiber industry. It is a further object to produce synthetic protein fibers of improved mechanical properties as compared to the properties of such fibers which have been subjected to the standard aqueous heat treatments of the textile industry. Since the handling and wearing characteristics of textile materials are affected by the loss in mechanical properties of the fiber from which the textile cloth is made, it is a still further ob- 2,828,131 Patented Mar. 25, 1958 ject to provide a process to prevent this loss of mechanical properties of the fiber and thus to yield a resultant textile material with improved handling and wearing characteristics.

These and other objects are accomplished by the practice of our invention. It has been found that the incorporation of from about 1% to about 4% of sodium oxalate in the aqueous baths used in the heat treatments of commercial synthetic protein fibers results in a substantial reduction of the normal loss of mechanical properties of the resultant fiber. This unusual and unexpected effect caused by the incorporation of from about 1% to about 4% of sodium oxalate in the aqueous heat-treatment baths yields fibers with markedly improved tensile strengths, good ultimate elongation, load extension curves which are normal, and the fibers show no signs of embrittlement or degradation.

Table I illustrates the effect of sodium oxalate on the mechanical properties of commercial zein fibers after soaking in water and sodium oxalate solution and steaming for about minutes at C. i. c. with steam at substantially atmospheric pressure.

Table I Soaked and Steamed Properties Tensile Ultimate Sodium Oxalate, percent pH Strength, Elongation,

g./d. percent Untreated Control 1.18 37 0 B 7 0. 72 68 7 0.93 46 4 7 0. 99 46 Saturated b 7 0.66

l Buffer solutions to maintain a pH of 7 were prepared according to Clark and Lubs, Handbook of Chem'mtry, Lange, 8th Edition, Handbook Publlshers, Inc. (1952), page 939.

b Suspended crystals were present in the treating bath.

e Ultimate elongation could not be determined because the sample was embrittled. Since in this experiment the treating bath contained a large amount of suspended sodium oxalate crystals, it is difficult to separate any possible effects of mechanical fiber damage, as for example when passing through the squeeze rolls, from the chemical eflect.

Table II illustrates the eifect of sodium oxalate at varying concentrations on the properties of commercial zein fiber when subjected to the aqueous heat-treatment with a standard 9% hydrogen peroxide bleach.

The color of each bleached sample was measured with a Hunter multipurpose rcflectometcr. The sample of tow was first attached to an open frame (similar to a small picture frame) with the fibers arranged parallel to the plane of the beam of light in the Hunter instrument. The 45, 0 reflectance was measured with a green filter, and then a blue filter. The ratio of the reflectance with these two filters, green/blue, represents a convenient measure of the yellowness oi a sample and is designated as yellowness index."

b Ulltgmat-e elongation was indeterminate because the sample was emritt e Suspended crystals were present in the treating bath.

It will be noted that as the concentration of sodium oxalate is increased from 1% to 4% there is a progressive improvement in tensile strength. Little change in color is produced by the presence or absence of sodium oxalate within this range of concentrations. In contrast, when a saturated solution is used, the strength loss is severe and the sample is embrittled. Since sodium oxalate is soluble only to a little over 4% it would not seem desirable to exceed this concentration.

In similar experiments in which commercial peanut protein fiber having a tensile strength of about 1.0 g./ denier, was steamed in the presence of 9% peroxide for 30 minutes at a pH of 8.2, the dry tensile strength of the fiber after treatment was 0.48 g./denier. The same commercial peanut protein fiber when steamed in the presence of 9% peroxide for 30 minutes at a pH of 8.2 but with 2% sodium oxalate added to the treatment bath had a resultant dry tensile strength of 0.54 g./denier. This peanut protein fiber steamed in the presence of oxalate also showed reduced plastering.

In normal practice in the textile industry it is difiicult to adjust and to maintain an aqueous treating bath at a given pH without the aid of buffering agents. This is even more true in the practice of our invention as the system oxalic acid-sodium oxalate butfers at a rather low pH. Accordingly it is desirable to add a modest quantity of a butter which will assist in maintaining the pH at the desired value. Our invention is not restricted to the use of any particular buffer. All of the well known bufiers of the art which will maintain the treating baths at a pH of from about 7 to about 8 are operable. This optimum pH was established in a study of the loss of mechanical properties which occurs when commercial zein fiber is steamed. Table III illustrates the effect of pH on the properties of zein fiber after steaming.

-Olark and Lubs bufiers (Res. above cited).

The oxalate is operable over a wide pH range but when color and mechanical properties are considered, as for example in bleaching, the optimum range is about pH 7 to 8.

For purposes of illustration, which should in no Way be construed as limiting the scope of our invention, Table IV is given to show the efiect of the use of the buffer, tetrasodium pyrophosphate, with sodium oxalate on commercial zein fiber in aqueous bleaching baths.

The results of the tests shown in Table IV clearly illustrate that the beneficial efiect of sodium oxalate is maximal in the range of about 2% to about 4%. A very small deleterious effect is noted on the tensile strength when 5% tetrasodium pyrophosphate is used with either 2% or 4% of sodium oxalate as compared to samples which were treated with these percentages of sodium oxalate alone. These very minor tensile losses can be tolerated, however, in view of the added advantage of ease of buffering the treatment bath within the desired range.

In order to substantiate the reliability of our invention for retaining the mechanical properties of synthetic protein fibers when these fibers are subjected to aqueous heat treatments, replicate experiments were performed upon zein fibers with and without sodium oxalate over a period of several weeks. In a system which contained 9% of hydrogen peroxide at pH 7 with no buffer or sodium oxalate present, the average strength was found to be 0.43 gram per denier, with a standard deviation of 0.01 gram per denier. When the treating medium was identical in composition, but contained 2% of added sodium oxalate, the average strength obtained was 0.85 gram per denier with a standard deviation of 0.06. In the presence of 5% of tetrasodium pyrophosphate, i. e., a bath which contained 9% of peroxide, 5% of tetrasodium pyrophosphate and 2% of sodium oxalate at pH 7, the average strength was 0.86 gram per denier with a standard deviation of 0.03. These results substantiate that the use of sodium oxalate gives a substantial and reproducible beneficial effect, while the presence of tetrasodium pyrophosphate produces little or no efiect on the mechanical properties, but it does act as a convenience in buffering the fiber treating medium.

In the practice of our invention, as described above, the sodium oxalate was prepared by neutralization of technical grade oxalic acid crystals with sodium hydroxide. Since the technical oxalic acid is readily available at a relatively low price it is believed that the use of this reagent is practical from a cost viewpoint. It was found that the cheaper technical sodium oxalate was so severely contaminated with dirt and impurities that its use with protein fibers was impractical.

The beneficial efiects reported herein for our process employing sodium oxalate are new, novel and unpredictable from anything previously reported in the art. The use of this reagent has been suggested in the bleaching of wool where the presence of small quantities of iron, for example, may cause severe local damage. In such cases, the use of an agent to sequester ferric ions is desirable. The results of tests afford strong evidence that sequestering action is not involved in the beneficial results obtained in the practice of this invention.

A possible clue to the nature of the effect of sodium oxalate lies, in the shrinkage which results during treat- T able IV Soak and Steam Properties H101, TSPP,- Sodium Tensile Ultimate Yellowness percent percent Oxalate, pH Strength, Elongation Index percent g./d. percent TSPP= tetras0dium pyrophosphate.

ment with peroxide bleaches. In a typical bleaching treatment in which a sample of commercial zein fiber was bleached at pH 7 with 9% of peroxide (but without the addition of sodium oxalate) the shrinkage during bleaching amounted to 15.7%. In a comparable bleaching treatment, to which, however, 4% of sodium oxalate had been added, the same samples shrank only 3.6%. These results suggest that the loss in strength during aqueous heat treatment is, in part at least, a result of loss of orientation due to shrinkage. The sodium oxalate may provide some type of temporary cross-links which prevent shrinkage. While no direct evidence for this hypothesis is presently available, the load-extension curves of samples treated in the presence of sodium oxalate do suggest that a larger number of cross-links remain in these fibers than in similar fibers treated in the absence of sodium oxalate.

We claim:

1. Process which comprises soaking a synthetic fiber formed of a protein of the group consisting of zein and peanut protein in a water solution containing from 1% to 4% of sodium oxalate, said solution having a pH of from about 7 to about 8, and thereafter steaming the 6 soaked fibers at a temperature of about 100 C. for at least about 30 minutes.

2. Process as defined in claim 1 in which the water solution of sodium oxalate contains about 9% of hydro gen peroxide.

3. Process as defined in claim 1 in which the protein is zein.

4. Process as defined in claim 1 in which the protein is peanut protein.

References Cited in the file of this patent UNITED STATES PATENTS 1,557,011 Blockey Oct. 13, 1925 1,765,581 Hall June 24, 1930 1,808,061 Palmer June 2, 1931 2,081,327 Franz May 25, 1937 FOREIGN PATENTS 246,879 Great Britain Feb. 1, 192% OTHER REFERENCES Reinthaler, Franz: Artificial Silk, 1928, p. 4. 

1. PROCESS WHICH COMPRISES SOAKING A SYNTHETIC FIBER FORMED OF A PROTEIN OF THE GROUP CONSISTING OF ZEIN AND PEANUT PROTEIN IN A WATER SOLUTION CONTAINING FROM 1% TO 4% OF SODIUM OXALATE, SAID SOLUTION HAVING PH OF FROM ABOUT 7 TO ABOUT 8, AND THEREAFTER STEAMING THE SOAKED FIBERS AT A TEMPERATURE OF ABOUT 100*C. FOR AT LEAST ABOUT 30 MINUTES.
 2. PROCESS AS DEFINED IN CLAIM 1 IN WHICH THE WATER SOLUTION OF SODIUM OXALATE CONTAINS ABOUT 9% OF HYDROGEN PEROXIDE. 